Topics in D-geometry

TL;DR

This work surveys D-branes on Calabi–Yau threefolds, linking boundary-state CFT techniques with large-volume geometric descriptions and presenting new results on marginal stability for the quintic. It articulates a geometric and a modified geometric hypothesis to explain how brane spectra depend on moduli, and examines how A- and B-branes, mirror symmetry, and period data organize BPS states across moduli. Key findings include partial matches between Gepner-model boundary states and large-volume predictions, the emergence of marginal-stability lines near the conifold, and a novel massless BPS state at non-singular moduli points that signals rich stringy corrections to the spectrum. The work outlines a program to test these hypotheses and to extend the framework to finite coupling and non-BPS configurations, with implications for phenomenology and the nonperturbative structure of string compactifications.

Abstract

We discuss the general theory of D-branes on Calabi-Yaus, recent results from the theory of boundary states, and new results on the spectrum of branes on the quintic CY. (Contribution to the proceedings of Strings '99 in Potsdam, Germany.)